hg5015:85484d35f1a2 now has a custom filter that will either call
the method and then convert to unicode or convert to unicode directly.
As an example I've added this to the msg contents in issue.item and msg.item.

So we are ready to release here because there is a good chance that only updates
to the template files itself are necessary now.

Like adding "|u" to a couple of places.
However to do this more systematically we should extend test_jinja2 to render
a few non-ascii example date over all templates.